Drop-in substitute for dichlorodifluoromethane refrigerant

ABSTRACT

A novel ternary mixture of refrigerants that can be drop-in substituted for dichlorodifluoromethane (R-12), but that, unlike dichlorodifluoromethane, causes very little ozone damage, comprising aproximately 2 to 20% by weight isobutane (R-600a), approximately 41 to 71% by weight chlorodifluoromethane (R-22), and aproximately 21 to 51% by weight chlorodifluoroethane (R-142b), with the weight percentages being of the overall mixture.

The present invention relates to refrigerants generally, and morespecifically to a mixture of refrigerants that may be substituted forthe environmentally damaging refrigerant dichlorodifluoromethane (R-12).

BACKGROUND OF THE INVENTION

Butane, isobutane, propane, and other hydrocarbons were commonly used asrefrigerants prior to World War II. The introduction of the family ofFREON® fluorocarbon products in the early 1930s provided nonflammable,nontoxic, and what were believed to be environmentally safe substituterefrigerants for hydrocarbons. Fluorocarbons largely supplantedhydrocarbons as refrigerants of choice in most applications followingWorld War II. Hydrocarbons are still in use today in special lowtemperature refrigeration systems (-100 degree Fahrenheit) due to therelatively high boiling points of fluorocarbons.

Certain chlorine containing fluorocarbon refrigerants, known aschlorofluorocarbons (CFC's), have been causally linked to thewell-documented depletion of the earth's ozone layer. The MontrealProtocol and the United States Environmental Protection Agency EPA) havethus called for a phase out of the use of the CFCs that are known to becontributing to the degradation of the environment, and specifically toozone layer depletion. Dichlorodifluoromethane (CCl₂ F₂), also known asCFC-12, Refrigerant-12, or simply R-12, is one of the most commonly usedCFC refrigerants in automobile air conditioners and elsewhere. It isalso the CFC refrigerant with the highest ozone depletion potential ofany known refrigerant. R-12 has an "ozone depletion units" (ODU) measureof 1.0, and serves as the yardstick of ozone depletion potential againstwhich all other refrigerants are measured.

New automobile air conditioners built in 1989 consumed 20 million poundsof R-12. An additional 80 million pounds of R-12 were consumed that yearin replenishing the R-12 refrigerant that leaked from existingautomobile air conditioners. Leaking of R-12 from automobile airconditioning systems is in fact a major source of the R-12 that escapesinto the atmosphere each year.

Since the discovery in the 1970's that CFC refrigerants escaping intothe atmosphere were depleting the earth's ozone layer, many companieshave spent large sums of money trying to develop a non-toxic,nonflammable replacement for R-12 that could be "dropped into" existingautomobile air conditioning systems as a substitute for R-12 withoutrequiring any equipment changes. To date, no such "drop in" substitutesfor R-12 have been announced. Consequently, the automobile industryplans to develop and market new automobile air conditioning systems bythe 1995 model Year that use an ozone safe refrigerant,tetrafluoroethane (CH₂ FCF₃), also known as, FC-134a, Refrigerant-134a,or simply R-134a. Fortunately, R-134a has an ozone depletion factor(ODF) of zero. Unfortunately, R-134a cannot be drop-in substituted forR-12 in existing air conditioning systems due to compressor lubricationproblems inherent in the use of R-134a in present systems, theinadequacy of the hoses used in present systems to handle R-134a, andthe necessity of using a larger compressor than is now in use with R-12refrigerant to Properly utilize R-134a.

Most automobiles that will be built through the 1994 model Year willstill require the use of an R-12 refrigerant, or an acceptable drop-insubstitute. With the environmental efforts to phase out, or ban, the useof ozone-depleting CFC's gaining momentum, it appears that an R-12drop-in substitute for use in existing air conditioning systems must befound.

SUMMARY OF THE INVENTION

The present invention provides a novel ternary mixture of refrigerantsthat can be substituted for R-12, but that, unlike R-12, causes verylittle ozone damage. It is free of R-12. The novel mixture ofrefrigerants of the present invention provides an acceptable level ofcooling in medium and high temperature applications where R-12 is now inuse, such as in coolers and air conditioners operating at evaporatingtemperatures of 25 degrees Fahrenheit and higher, i.e., automobile airconditioners. It also mixes well with compressor oils, thereby providingfor adequate lubrication of existing compressors that utilize R-12. Thenovel ternary mixture of refrigerants of the present invention istherefore a "drop-in" substitute for R-12.

One embodiment of the present invention comprises a ternary mixture ofrefrigerants that is a drop-in substitute for dichlorodifluoromethane(R-12), comprising about 2 to 20 weight percent isobutane (R-600a),about 21 to 51 weight percent chlorodifluoroethane (R-142b), and about41 to 71 weight percent chlorodifluoromethane (R-22), with the weightpercentages of the components being weight percentages of the overallmixture.

Another embodiment of the present invention comprises a method forproducing refrigeration in a refrigeration system designed for adichlorofluoromethane (R-12) refrigerant, comprising drop-insubstituting for the dichlorofluoromethane (R-12) a ternary mixture ofabout 2 to 20 weight percent isobutane (R-600a), about 21 to 51 weightpercent chlorodifluoroethane (R-142b), and about 41 to 71 weight percentchlorodifluoromethane (R-22), with the weight percentages of thecomponents being weight percentages of the overall mixture; condensingthe ternary mixture; and thereafter evaporating the ternary mixture inthe vicinity of a body to be cooled.

It is an object of the present invention to provide a "drop in"substitute for R-12 that causes very little ozone damage.

It is also an object of the present invention to provide a substituterefrigerant for R-12 that has an ozone depletion factor (ODF) ofapproximately 0.05.

It is also an object of the present invention to provide a drop-insubstitute refrigerant for R-12 that provides an acceptable level ofcooling in medium and high temperature applications where R-12 is now inuse, and that mixes well with compressor oils that are miscible withR-12 to provide for adequate lubrication of existing compressors thatutilize R-12.

Related objects and advantages of the present invention will be apparentfrom the following description.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments describedbelow, and specific language will be used to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the described embodiments, and such furtherapplications of the principles of the invention as described thereinbeing contemplated as would normally occur to one skilled in the art towhich the invention relates.

The novel ternary mixture of refrigerants of the present inventionincludes a mixture of approximately 2 to 20% by weight isobutane(R-600a), approximately 21 to 51% by weight chlorodifluoroethane(R-142b), and approximately 41 to 71% by weight chlorodifluoromethane(R-22), with the weight percentages totalling 100%. This novel mixtureof refrigerants is a drop-in substitute for R-12 in medium or hightemperature applications, such as coolers and air conditioners operatingat evaporating temperatures of 25 degrees Fahrenheit and higher.

Compared with R-12's ozone depletion factor (ODF) of 1.0, however, thisnovel mixture has an ozone depletion factor of about 0.05, and will beclassified as an EPA CLASS-II substance under the Federal Clean Air Act,as amended. R-12 is a CLASS-I substance. R-22 and R-142b are notproduction controlled or taxed by the EPA or under the Montreal Protocolat this time.

Typical air conditioning compressor operation produces a "fog"consisting of about 10% compressor lubrication (mineral) oil mixed inthe refrigerant discharge hot gas stream leaving the compressor. Therefrigerant typically condenses to liquid at temperatures of about 100to 180 degrees Fahrenheit. The warm refrigerant liquid lowers theviscosity of the oil it is carrying, so oil build up in the highpressure (liquid) side of the refrigeration circuit is not a problem.However, after passing through the expansion device, the refrigeranttemperature drops to the 32 to 35 degree Fahrenheit range and boils backto the gas phase in the evaporator. The oil will thicken and tend tobecome trapped in the evaporator if it is not readily miscible in therefrigerant. The refrigerant leaves the evaporator as a gas, leavingmuch of the oil behind, which then starves the compressor of oil andleads ultimately to compressor failure.

On the the other hand, an oil miscible refrigerant, such as R-12, causesthe oil and refrigerant to mix during the condensation phase. Thisgreatly lowers the viscosity of the oil during the evaporation phase.Since the oil contains large amounts of dissolved refrigerant, which isnow boiling and foaming, and is still low in viscosity, the oil getscarried out of the evaporator by the gas stream. Now in the warm suctionline, most of the remaining refrigerant leaves the oil. Since the gasvelocity is higher and the suction line is much warmer than theevaporator, the oil can find its way back to the compressor by creepingalong the walls of the warm suction line.

R-22 and R-142b are polar substances that have limited miscibility withthe compressor lubrication oils typically used in air conditioningsystems charged with R-12 refrigerant. In testing done to date withsamples of R-142b and R-22 mixed with approximately 10% by volume of a525 viscosity automotive refrigeration oil typically used in R-12systems, both R-142b and R-22 did not stay mixed with the 525 viscosityoil at evaporation temperatures (35 degrees Fahrenheit). Testing hasalso shown that R-12 refrigerant and the novel ternary mixture of thepresent invention stayed mixed with the 525 viscosity oil, even at 0degrees Fahrenheit.

It would be possible to use a binary mix of R-22 and R-142b in existingR-12 automobile systems, but the 525 viscosity oil used in R-12 systemswould have to be changed and replaced with an oil designed for use withan R-22 refrigerant. Oils designed for R-22 systems are usually of aviscosity of 150 to 300. To date, no commercially marketed 525 viscosityoil is known to be miscible with R-22 refrigerants. Due to the extremeconditions automotive air conditioners sometimes encounter, the use of150 to 300 viscosity oils may cause lubrication problems if the oilbecomes too thin.

Changing the oil in an existing R-12 system is also time consuming andcostly. Oil is spread out over the entire refrigeration circuit, sodraining the compressor will only get part (usually just 1/2) of the oilin the entire system. A common method of cleaning the oil from an R-12system is flushing the system with trichlorofluoromethane (CCl₃ F), alsoknown as R-11. This requires the inconvenience of disconnecting thesystem piping. Also, R-11 has the same ozone depletion factor as R-12,and it is becoming expensive and hard to find. Using several pounds ofR-11 to flush an existing R-12 system is therefore environmentallyunsound.

The isobutane component of the ternary mixture of the present inventionkeeps 525 viscosity oil miscible with the novel mixture of the presentinvention at evaporator temperatures, and also provides refrigerationeffect near the output side of the evaporator. Thus, the isobutanecomponent aids in the oil return from the evaporator back to thecompressor, and, in fact, is a necessary component to preventlubrication-related compressor failures in R-12 designed systems.

The small amount by weight of isobutane utilized in the mixture of thepresent invention does not appear to cause flammability problems. Incomparison testing with a binary mixture of isobutane and R-22, the R-22component of the ternary mixture of the invention appeared to leave theternary mixture more slowly when a system leak occurred, and did notconcentrate the isobutane to flammable limits. In the binaryisobutane/R-22 mixture, by contrast, the R-22 left the binary mixturequickly, concentrating the isobutane to flammable limits at the leaklocation.

Table I sets forth examples of ternary mixtures of the invention withknown tolerances to date. Percentages are weight percentages, andcomponents total about 100%.

                  TABLE I                                                         ______________________________________                                        Mixture                                                                              Isobutane    R-142b      R-22                                          ______________________________________                                        A      8%+/-2%      36%+/-2%    56%+/-2%                                      B      8%+10%-5%    36%+/-10%   56%+/-2%                                      C      8%+12%-6%    36%+/-15%   56%+/-15%                                     D      8%+/-2%      28%+/-7%    64%+/-7%                                      ______________________________________                                    

Mixture A has been the most preferred mixture to date. Mixture B wouldwork in most instances. However, mixtures at the high end of theisobutane range, and/or the high end of the R-142b range may lead toflammability problems in standard automobile air conditioning systemsdesigned for R-12. Also, mixtures at the low end of the isobutane range,and/or the low end of the R-142b range, may lead to compressor oilstarvation (poor oil return) and excessive system pressures when used inan automobile air conditioning system powered by an engine that is beingrevved while the automobile is not in motion on very hot days (90degrees Fahrenheit or hotter).

Mixture C will cause flammability problems in standard automobile airconditioning systems designed for R-12 when the R-142b and/or isobutanecomponents are at the maximum weight percentages. Low performance orliquid slugging may also occur. If the weight percentage for R-22 is atthe maximum, high system pressures will occur and lead to hoses burstingor other standard automobile air conditioning system failures. However,Mixture C may work well at the high and low ends of the component limitsin non automotive systems, such as household air conditioning systems orheatpumps, in R-22 systems, or in modified automobile air conditioningsystems designed for R-12. Mixture C may also work well at the high andlow ends of the component limits in standard automobile air conditioningsystems designed for R-12 that are operated only under specialconditions, such as at 60 degree Fahrenheit ambient temperature orlower.

Mixture D represents a high performance mixture that would deliver 50 to100% more cooling at higher temperatures. Mixture D would require minorequipment changes to the standard automobile air conditioning system toadd a high pressure cutoff switch to the high side (liquid) line gaugeservice port. The recommended cutoff pressure would be 375 to 400 PSIG,with a cut in pressure of 250 PSIG. Such a switch needs to be installedin series with the compressor clutch circuit to disable the compressorwhen the cut out pressure is reached. Revving an automobile engine whilenot in motion at an ambient temperature of over approximately 90 degreesFahrenheit would cause the cut out to operate. Engine idle speedsprobably will not cause a high pressure cut out if the condenser isclean. When the vehicle is in motion, ram air should provide adequatecondenser heat dissipation to prevent over pressure cut outs.

In testing completed to date, the ternary mixture of the invention hasexhibited much better cooling than R-12 at temperatures above ambienttemperatures (70-75 degrees Fahrenheit). On nonexpansion valve airconditioning systems found in most U.S. made vehicles (orifice only),head pressure of the ternary mixture of the present invention falls offbelow 70-75 degrees Fahrenheit, reducing the system capacity to whatwould be provided by R-12.

For the purpose of promoting a better understanding of and to furtherillustrate the invention, reference will now be made in the Examplesbelow to preferred ternary mixtures of refrigerants of the invention.

EXAMPLE 1

A mixture of 8.4% by weight isobutane, 35.7% by weight R-142b, and 55%by weight R-22 was provided in the following manner (the weightpercentages add up to 99.1% due to a measurement error). TIF electronicrefrigerant "charging" scales were used to weigh in the charge. A vacuumwas pulled on a Roninair 4 lb. capacity "dial-a-charge" refrigerantmeasuring cylinder. The isobutane (liquid) was weighed into the vacuumin the dial-a-charge. The pressure was about 26 PSIG at 73 degreesFahrenheit. The R-142b was then weighed into the dial-a-charge. R-22 wasthen weighed in slowly with intermittent shaking of the dial-a-charge tomix the isobutane and R-22 and noting of the pressure. R-22 was added inthis fashion until the pressure reading on the dial-a-charge wasapproximately 7 to 8 PSIG higher than what R-12 would have been at thetemperature of mixing. For this example, at 73 degrees Fahrenheit thepressure of 80 PSIG was used as the stopping point for adding R-22. R-22was added over a period of about 20 minutes to allow temperatures tostabilize within the dial-a-charge.

The dial-a-charge was then removed from the charging manifold/gauges andwas connected to the air conditioning system of a 1978 Datsun 810 andthe system was charged in the conventional manner. The oil in thissystem already contained a red dye for leak detection. Samples, underpressure, were taken with a vizi-charge from the liquid line duringoperation. The vizi-charge was then switched to the low (suction line),and the valve slowly opened to boil off the working fluid in order toobserve the amount of oil carried in the sample. About 10 to 12% byvolume of oil was observed after the refrigerant boiled off. Oil wasobserved to be still mixed evenly in the vizi-charge after setting for 3days.

The mixture within the dial-a-charge was tested for flammability, butcould not be ignited.

Cooling in the 1978 Datsun 810 seemed slightly better than that obtainedpreviously with R-12, although no detailed BTU measurements were taken.Suction (low side) and discharge (high side) pressures were close tothose obtained with R-12. At ambient temperatures in the low 70's, lowside pressure was about 11 to 13 PSIG (at 2000 rpm; R-12 would be about18 PSIG), and high side pressure was about 150 PSIG. Momentary high sidepressures were obtained around 200 PSIG with a hot engine, stopped attraffic lights, with the ambient temperature in the high 70's. This isclose to the high side pressures of R-12.

The air outlets within the automobile were emitting chilled air in the38 to 40 degrees Fahrenheit range, and the compressor was cycling on andoff due to the low temperature cut out being reached. The 1978 Datsun810 has the receiver (storage tank) in the high pressure side ratherthan in the low side as found in typical General Motors systems. Thelower suction pressures seemed to be due to the evaporator being colderby 5 to 7 degrees Fahrenheit than was the case with R-12.

EXAMPLE 2

Additional testing of the mixture of Example 1 was done in a 1990Pontiac Transsport equipped with a Harrison (GM) "V-5" variabledisplacement compressor. This compressor reduces its displacement(capacity) when the suction pressure drops below 28 PSIG. Compressor gasdischarge temperatures appeared to be close at idle with an ambienttemperature of 87 degrees Fahrenheit to those of an identical model 1990Pontiac Transsport at a new car dealer that utilized standard R-12refrigerant. The R-12 system idled at 150 degrees Fahrenheit and themixture of Example 1 idled at 154 degrees Fahrenheit.

Head (high side) pressures for the mixture of Example 1 were lower thanin the R-12 system when the vehicles were in motion (30 to 65 MPH),ranging from 220 to 150 PSIG at an ambient temperature in the low 90's.Racing the engine (2000 to 3000 RPM) while parked caused slightly higherhead pressures than the R-12 system. The R-12 system with MAX-AIRengaged was able to reach 400 PSIG at an ambient temperature of 100degrees Fahrenheit, but the mixture of Example 1 reached 400 PSIG at anambient temperature in the low 90's. This appears to be due to the factthat more heat is transferred and the condenser is less able to get ridof the heat with no ram air. At normal idle speeds and an ambienttemperature of 95 degrees Fahrenheit, head pressures of around 250 to260 PSIG were observed, well within system limits.

Increasing the weight percentage of R-22 in the mixture of Example 1tends to drive up head pressures and also moves more heat, leading tocooler discharge air. Idle performance with a higher R-22 weightpercentage produced pressures approaching design limits at ambienttemperatures of 95 degrees Fahrenheit or above. A pressure limiting cutout switch that would be connected t the high side service valve andwould be used to disengage the compressor if high idle or racing theengine while parked raised pressure too high (i.e., 375 PSIG) wouldprovide much superior cooling performance during normal operation.Cooling would be between 50% to 100% more than a comparable R-12 system.

Lowering the weight percentages of R-22 in the mixture of Example 1reduced the cooling capacity and lowered head pressure while raisingsuction pressure. On nonvariable displacement compressors, the suctionpressure would be expected to decrease instead of increase in this case.This moved the mixture toward increased flammability as well. Headpressures dropped significantly with the vehicle in motion to the pointof reducing refrigerant flow through the expansion device, which greatlyreduced cooling.

While the invention has been described in the Examples and foregoingdescription, the same is to be considered as illustrative and notrestrictive in character, it being understood that only preferredembodiments have been described and that all changes and modificationsthat come within the spirit of the invention are desired to beprotected.

What is claimed is:
 1. A ternary mixture of refrigerants that is adrop-in substitute for dichlorodifluoromethane refrigerant indichlorodifluoromethane refrigeration systems, comprising about 2 to 20weight percent isobutane, about 21 to 51 weight percent 1-chloro-1,1-difluoroethane, and about 41 to 71 weight percent chlorofluoromethane,with the weight percentages of said components being weight percentagesof the overall mixture.
 2. The ternary mixture of refrigerants of claim1 in which isobutane is present in about 6 to 10 weight percent,1-chloro-1, 1-difluoroethane is present in about 21 to 35 weightpercent, and chlorodifluoromethane is present in about 57 to 71 weightpercent, the weight percentages of said components being weightpercentages of the overall mixture.
 3. The ternary mixture ofrefrigerants of claim 1 in which isobutane is present in about 3 to 18weight percent, 1-chloro-1, 1-difluoroethane is present in about 26 to46 weight percent, and chlorodifluoromethane is present in about 46 to66 weight percent, the weight percentages of said components beingweight percentages of the overall mixture.
 4. The ternary mixture ofrefrigerants of claim 3 in which isobutane is present in about 6 to 10weight percent, 1-chloro-1, 1-difluoroethane is present in about 34 to38 weight percent, and chlorodifluoromethane is present in about 54 to58 weight percent, the weight percentages of said components beingweight percentages of the overall mixture.
 5. The ternary mixture ofrefrigerants of claim 1 in which said mixture is miscible withrefrigeration oils that are miscible with dichlorodifluoromethane. 6.The ternary mixture of refrigerants of claim 5 in which the weightpercentage of isobutane renders the mixture miscible with refrigerantsoils that are miscible with dichlorodifluoromethane.